1. Field of the Invention
This invention relates to the delivery of covers into registration with moving book blocks during a book binding operation. More particularly the present invention is directed to cover-feeding apparatus for incorporation into a book binding machine and especially to apparatus for efficiently and gently bringing in-fed covers, which have been withdrawn from a magazine, into alignment with continuously moving book blocks. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
The present invention is intended for use with book binding machines of the type employing book block grippers which may be moved continuously on an endless path. In such book binding machines, a transport apparatus, located below the plane of movement of the spines of the book blocks which are to be fitted with covers, receives the covers as individually separated from a magazine. The received covers are moved by the transport apparatus to a position where they are acquired by an alignment mechanism which propels each cover into alignment with a moving book block. Both the cover transport and the alignment mechanism include pusher devices which engage and apply force to the covers. Support surfaces are provided for the covers which are transported in an opened condition. During the alignment operation, the in-fed over is brought into alignment with the rear edge of the moving book block. After this alignment is achieved, the cover will be affixed to the book block.
German Patent 31 39 656 discloses an exemplary prior art cover-feeding apparatus. In the apparatus of this German patent, in order to achieve the requisite extremely accurate positioning of the covers against the book blocks, use is made of a pusher-equipped transport apparatus which is driven at a speed which is lower than the speed at which the book block grippers move. The movement of the pushers which engage the covers is coordinated with that of the book block grippers such that, when the alignment operation begins, the rear or trailing edge of the cover is in front of, i.e., is leading, the trailing edge of the moving book block in the direction of movement of both the cover and block. The alignment mechanism includes aligning elements which resiliently engage the rear edge of the cover. These aligning elements travel on a continuous path with their motion being synchronized with the movement of the book block grippers. The aligning elements project beyond the rear edges of the book block grippers and, as a result of the above-mentioned speed differential, overtake the cover from behind and acquire it from the pushers. Upon acquisition by the aligning elements, due to the resilient bias, the covers are accelerated and caused to move into alignment with the moving blocks. During this positioning, sudden variations in cover speed occur. These sudden variations in speed precipitate the possibility of the cover shooting forwardly beyond the desired alignment position. Accordingly, it is common practice to employ resiliently biased arresting means which frictionally engage the cover and thus prevent undesired erratic forward motion. The arresting means may, for example, be in the form of spring elements which engage the outer edges of the oppositely disposed "pages" or "leaves" of the cover.
A problem of long-standing in the art, which is particularly prevalent if the covers are of thin construction, is cover distortion as a result of the braking forces applied to the outer edges thereof by the arresting means at the same time a propelling force is exerted in the center region of the cover by the aligning elements. That is, the combination of the retarding and propelling forces, respectivly directed to the side edges and trailing edge of the cover during the alignment operation, may lead to an unstable equilibrium condition which presents the risk of a pronounced crushing effect on the cover.